1. Field of the Invention
The present invention is generally related to a method for cooling a marine engine and, more particularly, to a method for directing coolant through a multiple pass path through its cylinder head.
2. Description of the Related Art
Those skilled in the art of marine engines are familiar with many different types of cooling systems and many different techniques for removing heat from various heat emitting components of marine propulsion systems. Those skilled artisans are also familiar with many important issues associated with the removal of heat from marine engines. Not only is it important to avoid the overheating of various components and devices of a marine propulsion system, but it is also very important to avoid the removal of too much heat from certain portions of the engine. This is particularly true in marine engines, as opposed to engines used to propel land vehicles, because marine engines often use water from a body of water as its primary coolant and the water taken from lakes, rivers, bays, and oceans are often significantly colder than is desirable for maintaining the best operating temperatures of certain engine components. The use of cold water can often result in the overcooling of certain portions of the engine and, as a result, the condensing of fuel vapor which can dilute the oil supply of the engine with liquid fuel. The disadvantages of oil dilution are well known to those skilled in the art of marine engines as are the various types of damage that can result from it. Other problems associated with cooling marine engines relate to the direction of cooling water as it flows through engine components. Those skilled in the art of marine engines are also familiar with the importance of the sequence with which various engine to components are cooled.
U.S. Pat. No. 5,036,804, which issued to Shibata on Aug. 6, 1991, describes a cooling system for a four stroke outboard motor. The cooling system for a four cycle internal combustion engine utilized as a power plant for an outboard motor is described. The cooling system is designed so that coolant is first is delivered to cool an exhaust manifold in the cylinder block, then the exhaust port of the cylinder head and the other cylinder head components and then the cylinder block cooling jacket surrounding the cylinder bores.
U.S. Pat. No. 5,048,467, which issued to Kojima on Sep. 17, 1991, describes a water jacket arrangement for marine two cycle internal combustion engines. An outboard motor having an improved cooling system, wherein liquid coolant is circulated through an exhaust manifold cooling jacket then through a cylinder head cooling jacket and then through an upper portion of the cylinder block cooling jacket, is described. A thermostatic valve controls the flow from the upper cylinder block cooling jacket through a lower cylinder block cooling jacket so as to avoid quenching of the intake charge by coolant which has not reached operating temperature.
U.S. Pat. No. 5,873,330, which issued to Takahashi et al. on Feb. 23, 1999, describes a cooling arrangement for an engine. A cooling system for a vertically oriented engine of an outboard motor is disclosed. Coolant flows through the coolant system from a coolant pump into a coolant jacket surrounding an exhaust manifold of the engine, down to a bottom of a cylinder head of the engine, through a cylinder head, an engine block, through a thermostat, and then to a jacket positioned along an exhaust pipe leading from the exhaust manifold, to a coolant discharge.
U.S. Pat. No. 5,904,605, which issued to Kawasaki et al. on May 18, to 1999, describes a cooling apparatus for an outboard motor. The outboard motor is provided with a water cooled engine in a vertical alignment in which a crankshaft is vertically disposed, the engine being composed of a cylinder block, a cylinder head and an exhaust manifold into which water jackets are formed respectively and the water jackets are supplied with cooling water from a water pump disposed below the engine, the cooling apparatus comprising a cylinder cooling water passage for supplying cooling water from the water pump to the water jackets of the cylinder block and the cylinder head. It also comprises an exhaust cooling water passage for supplying cooling water from the water pump to the water jacket of the exhaust manifold, the cylinder cooling water passage and the exhaust cooling water passage being independently disposed from each other and being joined together at downstream portions thereof.
U.S. Pat. No. 6,890,228, which issued to Tawa et al. on May 10, 2005, describes an outboard motor equipped with a water cooled engine. It includes an exhaust manifold cooling water jacket for cooling an exhaust manifold for discharging to the outside exhaust gas from a combustion chamber. The manifold cooling water jacket is supplied with cooling water from a cooling water pump. A water outlet is provided in the highest part of the exhaust manifold cooling water jacket and is made to communicate with a water check outlet for confirming the circulation of cooling water due to operation of the cooling water pump.
U.S. Pat. No. 6,921,306, which issued to Tawa et al. on Jul. 26, 2005, describes a water cooled vertical engine and outboard motor equipped therewith. It includes an exhaust guide cooling water jacket and an exhaust manifold cooling water jacket which are formed in an engine compartment. It also comprises a cylinder block cooling water jacket formed in a cylinder block. Water is supplied from a cooling water pump in parallel to an upper part and a lower part of the cylinder block cooling water jacket through the exhaust guide cooling water jacket and the exhaust manifold cooling water jacket.
U.S. Pat. No. 7,114,469, which issued to Taylor on Oct. 3, 2006, discloses a cooling system for a marine propulsion engine. The system divides a flow of cooling water into first and second streams downstream of a pump. The first stream flows through a first cooling system which is controlled by a pressure sensitive valve. The second stream flows through a second cooling system which is controlled by a temperature sensitive valve.
U.S. Pat. No. 7,264,520, which issued to Taylor et al. on Sep. 4, 2007, discloses a cooling system for an outboard motor having both open and closed loop portions. The system pumps water from a body of water through certain selected portions of the outboard motor and through a heat exchanger which, in turn, comprises a coolant conduit that is directed to conduct the coolant in thermal communication with various portions of the outboard motor. The engine block is cooled by a flow of the coolant and an engine head is cooled by a flow of water from the body of water. Other head emitting devices are connected in thermal and fluid communication with the water and coolant conduits.
U.S. Pat. No. 7,318,396, which issued to Belter et al. on Jan. 15, 2008, discloses a cooling system for a marine propulsion engine. It incorporates first and second thermally responsive valves which are responsive to increases in temperature above first and second temperature thresholds, respectively. The two thermally responsive valves are configured in serial fluid communication with each other in a cooling system, with one thermally responsive valve being located upstream from the other.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
It would be beneficial if a cooling system for a marine engine could remove heat from selected portions of the engine system sequentially in a preferred order that prevents overcooling of certain components while assuring that sufficient heat is removed from other components. In addition, it would be beneficial if this type of cooling system could avoid the entrapment of air pockets within the coolant flow that could otherwise result in the overheating of local regions of the engine system. In addition, it would be beneficial if various portions of the engine could be cooled in a manner that tailors the amount of heat removed from various regions of the engine by governing the magnitude of coolant flow in a preselected proportion that is selected as a function of the type of engine and the relative heat emitted by the various regions of the engine.